Left and right lighting systems for large panel trucks, semi-trailers and the like have traditionally been supplied with electrical current via a single cable with multiple individual insulated conductors arrayed therein. For example, depending upon vehicle lighting complexity and accessories, six, seven or more individual conductors are contained in the single cable, which extends from a standard "nose box" on the front of the truck or trailer to the lighting and accessory systems on the rear and side of the truck or trailer. Of the conductors in the cable, four or five are dedicated to the lighting systems, with a white wire providing a common ground. Of the four or five lighting wires, brown and black are both common conductors feeding left and right marker and tail lights, red is a common conductor feeding left and right stop lights, green is a dedicated conductor feeding a curbside turn signal, and yellow is a dedicated conductor feeding a roadside turn signal. An additional blue conductor is often included for anti-lock braking systems.
Since four of the wires are common to both left and right lights, a junction plug must be provided at the rear terminus of the multi-conductor cable to split each of the common conductors to left and right conductors. Furthermore, the provision of common wires running the length of the truck or trailer means that heavier gauge conductors must be used to minimize resistance, e.g. 12 gauge wire is required for the common conductors in a typical semi-trailer.
This typical truck or trailer wiring arrangement presents a number of problems. Due to the relatively heavy gauge conductors needed, the multi-conductor cable is fairly rigid and inflexible, thus creating problems as it is bent around obstacles or fed through openings. The heavier gauge conductors are also more expensive. The junction plug which is required for splitting the common conductors between left and right circuits is expensive, adds resistance and is subject to moisture penetration and accompanying corrosion. Additional labor is required for installing, testing and providing moisture protection for the junction plug, which also adds to a manufacturer's cost.
It is clear that a need exists for an improved wiring system and method for vehicles and trailers. Such an improved system should allow the use of smaller gauge, and therefore more flexible multi-conductor cables and should eliminate any junction plug required for splitting common conductors into separate left-right circuits.